In recent years, techniques for reducing parasitic capacitance have been under development in order to enhance the performance of semiconductor devices. The techniques for reducing parasitic capacitance include an SOS (silicon on sapphire) structure. There is a method for producing the SOS structure by bonding substrates made of different materials together. Examples of a method for bonding substrates made of different materials together include a technique described in Japanese Unexamined Patent Application Publication No. 2004-343359 and a technique described in Japanese Unexamined Patent Application Publication No. 2005-104801. In these patent publications, two substrates made of different materials are bonded together in such a manner that a metal intermediate layer is provided between the substrates.
However, in the case of using the technique described in Japanese Unexamined Patent Application Publication No. 2004-343359 or 2005-104801 to form an SOS structure, a metal making up the metal intermediate layer may possibly diffuse into silicon, which is to be formed into a functional layer of a semiconductor device, to adversely affect the operation of the semiconductor device.
The present invention has been devised under the foregoing circumstances. It is an object of the present invention to provide a composite substrate in which the diffusion of metal into a semiconductor layer is suppressed and a method for manufacturing the same.
A composite substrate according to an embodiment of the present invention includes a supporting substrate composed of an insulating material, a semiconductor layer composed of a single-crystalline semiconductor, and interfacial inclusions. The semiconductor layer is overlaid on the supporting substrate and is bonded to the supporting substrate. The interfacial inclusions with a density of 1012 atoms/cm2 or less are present at an interface between the supporting substrate and the semiconductor layer and are composed of a metal element different from elements composing up the supporting substrate and the semiconductor layer.
A method of manufacturing a composite substrate according to an embodiment of the present invention includes an activating step and a bonding step. In the activating step, a surface of a supporting substrate and a surface of a semiconductor layer activated in a vacuum vessel using a FAB gun in such a state that the surface of the supporting substrate and the surface of the semiconductor layer do not face each other. In the bonding step, the supporting substrate and the semiconductor layer bonded together at room temperature in such a manner that a first surface activated of the supporting substrate is brought into contact with a second surface activated of the semiconductor layer.
According to the present invention, a composite substrate including a semiconductor layer in which the diffusion of metal is suppressed can be provided.